\documentclass{book}
\usepackage{glossaries-extra}

\setlength{\parindent}{0pt}
\newacronym[\glslongpluralkey={dynamic-link Libraries}]{dll}{dLL}{dynamic-link Library}

\begin{document}
\glsunset{dll}

Manual use of glsuppercase: \glsuppercase{\glsentrytext{dll}}\\
GLS: \GLS{dll}, GLSpl: \GLSpl{dll}\\
GLStext: \GLStext{dll}\\
GLSfirst: \GLSfirst{dll}\\
GLSplural: \GLSplural{dll}

\end{document}
